Dual state mirror assembly

ABSTRACT

A dual state mirror assembly for use with motor vehicles includes a housing having an open front for receiving an outer substrate to form an enclosure. The outer substrate has a surface coated with a thin metal film to act as a beam splitter. An inner substrate having a reflective front surface is mounted within the enclosure so that in a first position, the inner substrate is in direct contact with the outer substrate, to produce a single bright reflected image, and so that in a second position, the inner substrate is placed at an angle with respect to the outer substrate, to provide a dimmed image and to minimize glare.

BACKGROUND OF THE INVENTION

The present invention generally relates to a dual state mirror assemblyfor use with automobiles, trucks, buses and other types of vehicles,primarily as a rearview mirror. The dual state mirror of the presentinvention is particularly useful as an exterior mirror for largertrucks, including those in classes 6, 7 and 8, as well as buses, andwill be described in this general context for convenience ofillustration. However, the general principles described will also beuseful in conjunction with other types of mirrors, for various types ofvehicles, and for other applications such as laser technology.

Early attempts to reduce the glare associated with rearview mirrors forvehicles included the use of prismatic features, and electronicfeatures, including electrochromic and dichroic liquid crystal displaytechnologies.

In the case of prismatic technology, the rearview mirror is providedwith two independent states of reflectance using a prismatic elementincluding a high reflectance surface for daytime use, and a lowreflectance surface for nighttime use. To operate such a mirror, thedriver manually adjusts the position of the prismatic element, dependingupon the time of

In both positions the driver actually views both prism surfaces, withdifferent images. In the daytime position, the high reflectance surfaceyields sufficient light to make the dimmer image on the low reflectancesurface unnoticeable. In the nighttime position, the high reflectancesurface is pointed to a dark region in the vehicle (typically the roof)so as not to interfere with the dimmer image on the low reflectancesurface.

In the case of electrochromic and dichroic liquid crystal displaytechnologies, the dimming function is achieved electronically, and istherefore automated.

All of these methods, however, have some key drawbacks. Mirrors thatincorporate prismatic surfaces suffer from unpredictable opticalquality. If the lighting conditions inside the vehicle become less thanoptimum (i.e., vehicles travelling closely behind and illuminating theinterior), the rearview mirror can produce multiple images. Moreimportantly, prismatic mirrors can not be used for exterior applicationssince there is no satisfactory dark region to which the high reflectancesurface can be directed.

Electrochromic mirrors also tend to produce multiple images. Inaddition, such mirrors have slow response times and tend to alter thecolor of the reflected images. Although electrochromic mirrors can beused as exterior mirrors, they are very costly for the relatively largeareas associated with exterior mirror applications (particularly forlarger vehicles such as trucks and buses).

The use of dichroic mirrors is essentially precluded by regulation. In1992, the U.S. National Highway Traffic Safety Administration (NHTSA)issued a regulation that all multiple reflectance mirrors revert to ahigh reflectance state in the event of electrical failure. Thiscondition could not be effectively met with dichroic mirrors.

Earlier efforts to develop a useful dual state rearview mirror, prior toelectrochromic and dichroic LCD technologies, employed paired, plateglass elements to achieve the desired result. Examples of these devicesmay be found with reference to U.S. Pat. Nos. 3,574,446 (Moore);3,836,235 (Russell); 4,371,235 (Locke, Sr.); and 4,560,259 (Russell).Each of these mirror systems includes an enclosure with a plate glassface, and a mirrored element positioned within the enclosure and spacedfrom the plate glass face. The mirrored element is capable of movement(i.e., rotation) between daytime and nighttime positions which areprimarily determined by the position of the mirrored element relative tothe plate glass face of the enclosure.

However, in each case, the disclosed devices are provided with substratesurfaces (plate glass and mirror) which are spaced apart. In addition,the disclosed devices are provided with plate glass and mirroredelements that do not allow for adjustment of the reflective andtransmissive properties of the overall system. As a consequence, none ofthese devices are particularly satisfactory in actual operation. Doubleimages are not uncommon, and the difference between the reflected imagesthe different mirror surfaces (i.e., elements in parallel, in a daytimemode position) is so great that nighttime use (while in a highreflectance, daytime configuration) is seriously compromised.

SUMMARY OF THE INVENTION

It is therefore the primary object of the present invention to remedythe disadvantages of prior dual state mirrors.

It is also an object of the present invention to provide a dual statemirror which exhibits proper reflectance characteristics for promotingboth daytime and nighttime use.

It is also an object of the present invention to provide a dual statemirror which provides satisfactory daytime and nighttime modes ofoperation without being subject to double images.

It is also an object of the present invention to provide a dual statemirror having the foregoing improvements, yet which is simple andinexpensive in construction, as well as reliable and easy to use.

In accordance with the present invention, these and other objects whichwill be apparent are achieved with a tandem mirror assembly having outerand inner substrates mounted in a specified configuration. In apreferred embodiment, the outer substrate is semi-transparent, and maybe configured as a beam-splitter. As an example, the outer substrate maybe implemented as a glass substrate having a thin film coating thatproduces a low reflectance, semi-transparent (mirrored) surface. Theinner substrate is reflective, and may be implemented as a thin filmcoating that produces a high reflectance (mirrored) surface. The innersubstrate is movable relative to the outer substrate (which ispreferably static) to develop two independently selectable states ofreflectance. In one state, the substrates are in direct contact witheach other, for daytime use. In the other state, the substrates areangled relative to each other, for nighttime use. When the substratesare in direct contact (i.e., the first, daytime state), the mirrorassembly combines to produce a high reflectance image which is void ofmultiple images. When the substrates are angled with respect to oneanother (i.e., the second, nighttime state), the mirror assemblycombines to produce an enhanced, partially reflective image which isvirtually free of glare.

Preferably, the outer substrate is formed of a conventional, transparentmaterial coated with a thin metal film or multiple thin metal films todevelop a partial reflectance. Coating materials including indium tinoxide, aluminum and chrome, or a similar material capable of producing anominal specular reflectance of 15% for incident light in the visiblespectrum, and nominal transmissive values on the order of 75% forincident light in the visible spectrum, may be used for such purposes.The inner substrate is preferably formed of a conventional glass, metalor plastic substrate, or a similar, mechanically rigid material that canbe mirrored, provided with a thin film coating (on its front surface)capable of producing a nominal reflectance of 90% for visiblewavelengths of light. Optionally, the inner substrate may be developedsuch that the reflectance lies in a range between 60% and 95%. In thisway, as distinguished from solid state mirrors which have a limitedreflectance range, the mirror assembly of the present invention cansimultaneously develop both maximum (>80%) and minimum (<15%)reflectance values, as desired.

Such a device is ideally suited as an externally mounted, rearviewmirror for large trucks categorized by classes 6, 7 and 8, as well asbuses, where the characteristics of the substrates and theirrelationship to each other (and relative to the driver) are particularlyimportant. This is because unlike previous mirror assemblies, the mirrorassembly of the present invention includes an outer substrate in whichthe reflectance and the transmissivity values can be adjusted, promotingnighttime use, and is implemented as a dual substrate assembly in whichthe outer substrate and the inner substrate are placed in direct contactwith each other, promoting daytime use.

The foregoing mirror assembly is preferably implemented within a casingfor receiving the outer and inner substrates. It is an important featureof the present invention that the substrates are contained within thecasing and in contact with each other, and that the means which areprovided to move (rotate) the inner substrate operate to angle the innersubstrate away from the outer substrate, to develop the low reflectancestate. In this angled position, only the image of the outer (lowreflectance) substrate is observed by the driver, so that no reflectedlight from the inner substrate is observed. The driver, therefore, seesa dimmed (anti-glare) version of the original image (i.e., a vehicle'sheadlights).

Such movement can be controlled mechanically, by a simple lever, orelectrically, by a solenoid (or solenoids) housed within the casingwhich receives the mirror assembly. In a preferred embodiment, thesolenoid, when energized, extends a plunger that applies a force to theinner substrate relative to its axis of rotation (using, for example, atubular push-type solenoid). A spring is used to provide forces forreturning the inner substrate to its initial position, in contact withthe outer substrate. The solenoid preferably operates in conjunctionwith a locking mechanism for maintaining the inner substrate in itsclosed position, in direct contact with the outer substrate. Such anassembly operates to place the mirror assembly of the present invention(whether mechanically or electrically implemented) in compliance withthe above-mentioned safety standards established by the U.S. NationalHighway Traffic Safety Administration.

Optionally, a miniature DC motor could be used as an actuator for movingthe inner substrate to the low reflectance state. A cooperating returnspring mechanism would again be required to ensure that the mirrorassembly reverts to a high reflectance state in the event of a powerinterruption. Miniature air-operated or hydraulically-operated pistonscould similarly be used to move the inner substrate relative to theouter substrate, as well as other types of solenoids, includingpull-type solenoids, as well as box-type and U-type solenoids.

Irrespective of its manner of implementation, the mirror assembly of thepresent invention may additionally be provided with a conventionalmirror heating device, for de-icing purposes.

For further discussion of the dual state mirror assembly of the presentinvention, reference is made to the detailed description which isprovided below, taken in conjunction with the following illustrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a casing for housing the mirrorassembly of the present invention, showing the mirror assembly in aposition suitable for daytime use.

FIG. 2 is a partial sectional view of the two substrates comprising themirror assembly.

FIG. 3 is a cross-sectional view similar to FIG. 1, showing the mirrorassembly in a position suitable for nighttime use.

FIG. 4 is an exploded elevational view of components of the rotationmechanism.

FIGS. 5 and 6 are cross-sectional views similar to FIGS. 1 and 3,showing the mirror assembly in intermediate operating positions.

FIG. 7 is a graph showing a series of curves which illustrate solenoidplunger pushing forces as a function of the distance of the plunger fromits fully seated position.

FIG. 8 is a schematic diagram of a preferred electrical circuit foroperating the mirror assembly of the present invention.

FIG. 9 shows an overall system for implementing the improvements of thepresent invention.

FIG. 10A is a schematic illustration of the optics of the mirrorassembly of the present invention in a daytime mode of operation.

FIG. 10B is a similar schematic illustration of a prior dual statemirror assembly in a daytime mode of operation.

FIG. 11A is a schematic illustration of the optics of the mirrorassembly of the present invention in a nighttime mode of operation.

FIG. 11B is a similar schematic illustration of a prior dual statemirror assembly in a nighttime mode of operation.

FIG. 12 is a schematic illustration showing optical characteristics fora spaced pair of substrates.

FIG. 13A, 13B and 13C are schematic illustrations of different imagesformed with a mirror, a spaced pair of substrates, and paired substratesimplemented in accordance with the present invention, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The improvements of the mirror assembly of the present invention aregenerally achieved using two mirrored substrates mounted within a case(i.e., a housing). The drawings submitted herewith illustrate a casesuitable for use as an outside rearview mirror for a truck or bus, andfurther discussion will proceed based upon this illustrated embodiment.However, it should be understood that this represents only one of avariety of applications for the mirror assembly of the presentinvention. other housings, and other implementations of the mirrorassembly may be developed for similar applications (i.e., trucks andbuses), including both left-side and right-side rearview mirrors, aswell as for other types of vehicles (e.g., small trucks andautomobiles), or for other applications (e.g., laser technologies). Suchhousings and mirror assemblies may be configured to suit the environmentin which they will be used. Consequently, the following discussionshould not be taken as a limitation to the potential applications forthe improvements of the present invention.

Referring now to FIGS. 1 through 6, the case 1 is implemented as aleft-side, rearview truck mirror. The case 1 is semi-cylindrical inshape and may be formed of any material suitable for exposure to theelements. Suitable end caps (not shown) can be provided to finish theends of the housing, or shaped, integral ends may be used to finish thehousing, as desired. The size of the housing will vary with the size ofthe mirror which is preferred for a particular application, or aparticular make and model vehicle.

An outer (low-reflectance) substrate 5 is mounted in fixed position tothe case 1, completing an enclosure which is preferably sealed to theelements. To this end, edge portions 5' of the outer substrate 5 areheld against the flanges 3' of a frame 3 (i.e., a face plate). Gaskets 4are provided to seal the outer substrate 5 to the frame 3. The frame 3is in turn attached to the case 1 (e.g., by rivets 1a or other suitablefasteners for engaging blind holes 1b provided in the case 1).Additional gaskets 2 are preferably situated between the frame 3 and thecase 1 to complete a seal which is suitable for preventing rain, dust,salt or other contaminants from entering the housing and reaching thestructural elements of the mirror assembly.

In its preferred embodiment, the outer substrate 5 is configured as abeam-splitter (i.e., having partially transmissive and partiallyreflective characteristics), and is implemented as a transparent ortranslucent plate provided with suitable front and back coatings. Forexample, referring to FIG. 2, the rear surface of a glass plate can becoated with a thin metal film (shown at 27) or multiple films (includingindium, tin, aluminum, chrome and nickel, as well as combinations ofthese materials and their oxides) capable of producing a nominalspecular reflectance of 15% for incident light in the visible spectrumand a nominal transmissivity of 75% for incident light in the visiblespectrum. The thin metal film 27 may further be provided with aprotective, transparent over-coating to protect against mechanicalabrasion and/or degradation of the thin metal film 27 due to theenvironment. One such material for implementing this protectiveover-coating is silicon oxide (SiO).

The rear surface of the glass plate is optionally coated to producevaried reflectance values of between 10% and 30%, and to developcorresponding transmissivity values of between 80% and 60%,respectively. Such coatings can be uniformly applied to the glass plate,or selectively applied to the glass plate to form a segmented substrate,if desired. The combination of reflective and transmissive values can bevaried, as needed, depending upon the intended application for themirror assembly. In such case, the characteristics of the thin metalfilm 27 can be varied, or multiple films can be used, to achieve a rangeof useful reflective and transmissive values.

The thickness of the outer substrate 5 may vary, but is preferablybetween 0.062 and 0.125 inches. The front surface of the outer substrate5 can additionally be provided with an anti-reflective coating 28, tominimize front surface reflections. Such coatings will typically developa reflectance on the order of less than 4%.

Positioned directly behind the outer substrate 5, and housed within thecase 1, is an inner (reflective) substrate 6. The inner substrate 6 ispreferably implemented as a front surface, reflecting mirror. Forexample, and referring again to FIG. 2, the front surface of a glassplate can be coated with a thin film (shown at 26) capable of producinga nominal reflectance of 90% for visible wavelengths of light. Again,such coatings can be uniformly applied to the glass plate, orselectively applied to the glass plate to form a segmented substrate, ifdesired. The values for this reflectance may vary between 60% and 95%,as desired. The thickness of the inner substrate 6 may also vary, but ispreferably between 0.062 and 0.125 inches.

The inner substrate 6 is attached to a mechanism for moving (i.e.,rotating) the inner substrate 6 relative to the outer substrate 5,between a daytime position (shown in FIG. 1) in which the innersubstrate 6 is in direct contact with the outer substrate 5 and anighttime position (FIG. 3) in which the inner substrate 6 is placed atan angle relative to the outer substrate 5. In accordance with thepresent invention, and as will be discussed more fully below, the innersubstrate 6 is preferably moved relative to the outer substrate 5 alongcontiguous, lateral edges of the substrates 5, 6 to facilitate directcontact between the substrates 5, 6 when placed in the daytime operatingposition.

The substrates 5, 6 of the present invention will typically be flat, butcan also be made convex in shape to create a convex dual state mirror.In such case, the rear surface of the outer substrate and the frontsurface of the inner substrate would be provided with matching radii toensure proper surface contact between the two substrates when in theclosed position (to develop the high reflectance state). This can beaccomplished by "sagging" glass onto matching tools, using techniqueswhich are themselves known (e.g., a glass plate is placed on a shapingtool and heated until it sags onto the tool, taking the shape of thetool).

The case 1 can be fabricated in any of a variety of ways, but ispreferably formed as a single piece, either from a molded plastic orfrom sheet metal. As previously indicated, the case 1 can also befabricated from multiple pieces which are suitably assembled, ifdesired. Regardless of its manner of fabrication, the case 1 must beconfigured to allow sufficient space for the inner substrate 6 to rotateaway from the outer substrate 5, to an appropriate angle, and for themechanism which is used for such purposes. The case 1 is furtherpreferably configured to assume an aerodynamic shape, to reduce windresistance resulting from placement of the rearview mirror on thevehicle. The inner surface of the casing, which can be exposed reflectedlight as the inner substrate 6 is rotated away from the outer substrate5, is preferably formed as a non-reflecting, light absorbing surface,and is therefore typically provided with a flat black finish (orequivalent). This assists in preventing the glare of reflected light,and in eliminating extraneous light or images observed by the driver, aswill be discussed more fully below.

If desired, the frame 3 of the case 1 can be provided with a sub-frame,to allow for the convenient cleaning of any contaminants that may cometo accumulate and become visible on the substrates 5, 6 over time. Sucha sub-frame could easily be removed (using, e.g., a set of quickdisconnect fasteners) to expose the rear surface of the outer substrate5 and the front surface of the inner substrate 6, to allow for theircleaning.

In its preferred embodiment, the rotation mechanism includes a supportassembly comprised of a mounting plate 8, a mounting arm 10 and alocking bracket 15 which cooperate to receive the inner substrate 6.These components, in conjunction with a locking mechanism which will bedescribed more fully below, cooperate to move the inner substrate 6relative to the outer substrate 5, between a closed position in whichthe substrates 5, 6 are in direct contact (daytime mode) and an openposition in which the substrates 5, 6 are placed at an angle to eachother (nighttime mode).

The mounting plate 8 preferably receives the inner substrate 6 in arecessed portion for seating the inner substrate The inner substrate 6can be attached to the mounting plate 8 by any of a variety ofconventional attachment devices including the double-faced foam tape 6ashown in FIG. 2, as well as epoxies, glues or the like, or mechanicalfasteners and brackets. The mounting plate 8 further includes a hinge 11for engaging a pivot 12 associated with the mounting arm 10. Springs 9are situated on either side of the hinge 11 and pivot 12 so that whenthe substrates 5, 6 are not in contact, the mounting plate 8 isprevented from rotating freely at the hinge 11, and so that when thesubstrates 5, 6 are moved into the daytime position, a direct (parallel)contact is established between the substrates 5, 6. One or more mountingarms 10 may be provided for engaging the mounting plate 8, dependingupon the length of the substrates 5, 6 and the conditions under whichthe mirror assembly will be used. The locking bracket 15 may be fixed toany one of the mounting arms 10 which may be provided, or plural lockingbrackets 15 may be fixed to selected mounting arms 10, as desired.

The mechanism which is provided for moving the inner substrate 6relative to the outer substrate 5 further includes a locking mechanismwhich operates to manipulate the foregoing components, between a lockedand an unlocked position. As is additionally illustrated in FIG. 4, thelocking mechanism generally includes a mounting bracket 16 and anassociated slider linkage 21. The slider linkage 21 is preferably formedas a narrow, flat metal band having an extended oval slot 24' forengaging a shoulder screw 24 extending from the mounting bracket 16. Themounting bracket 16 is further rotatably connected to the mounting arm10 (or arms) at a pivot 13, for engaging an aperture 13' formed in themounting bracket 16.

A solenoid 18 is fitted to the mounting bracket 16 using, for example,the mounting bracket 22, and operates to rotate the inner substrate 6about one of its lateral edges (the edge closest to the driver). To thisend, the mounting arm 10 (or arms) is rotated relative to the mountingbracket 16, about the pivot 13, responsive to operations of the solenoid18. As previously indicated, the mounting plate 8 is afforded a limiteddegree of independent motion (pivoting movement) relative to themounting arm 10 (or arms). By rotating the inner substrate 6 along alateral edge contiguous with the corresponding lateral edge of the outersubstrate 5, and by allowing the inner substrate 6 to pivot relative tothe outer substrate 5, the inner substrate 6 is caused to come into fullcontact with the outer substrate 5, along its full surface, irrespectiveof which portions of the substrates first touch during closure. Suchrotation preferably occurs in less than one second (to avoid distractingthe driver), and is readily accomplished by applying a nominal voltageto the solenoid 18.

The solenoid 18 includes a plunger 19, which is caused to move linearlyin the general direction of the pivot 13. The plunger 19 is fitted witha coupling 23, which is attached to the plunger 19 using, for example,set screws or similar attachments. The coupling 23 includes a shoulderscrew 14 for simultaneously engaging a slot 14' formed in the mountingbracket 16 and an aperture 14" formed in the slider linkage 21 (see FIG.4), to complete the mechanical connection between the mounting bracket16 and the slider linkage 21, and the mounting arm 10 (or arms). Theslots 14', 24' and shoulder screws 14, 24 operate to confine the sliderlinkage 21 to linear movements along the longitudinal axis of themounting bracket 16.

The slider linkage 21 further includes a roller bearing 20 (attached ata predetermined distance of approximately 3 inches from the pivot 13)for engaging the locking bracket 15 (or brackets) associated with themounting arm 10 (or arms), and a shoulder screw 17 for receiving aspring 25. The spring 25 is similarly received by the mounting bracket16 (using a similar shoulder screw 17), and is preferably sized toprovide a return force of approximately 2 lbs. The return force of thespring 25 will in turn act on the roller bearing 20, through the sliderlinkage 21.

In operation, the components of the locking mechanism 16, 21 interactwith the support assembly 8, 9, 10 and the locking bracket 15 toappropriately bias the mounting arm 10, and accordingly, the innersubstrate 6. Such components are normally biased to urge the innersubstrate 6 into contact with the outer substrate 5. To this end, theslider linkage 21 is urged in a direction away from the pivot 13 by thespring 25. The direction of the resulting force is generally along theline of action of the spring 25, in line with the mounting bracket 16and the slider linkage 21. The top surface 15' of the locking bracket 15is sloped to allow for smooth interaction with the roller bearing 20 ofthe slider linkage 21, which slides along the locking bracket 15. Whenthe inner substrate 6 is in contact with the outer substrate 5, theslider linkage 21 is pulled back by the spring 25 and the roller bearing20 engages the sloped top edge 15' of the locking bracket 15. The returnforce developed by the spring 25 urges the roller bearing 20 against thesloped top surface 15' of the locking bracket 15, applying a forcedirectly to the locking bracket 15. This force is applied in adirection, and at a distance (e.g., of approximately 3 inches) from thepivot 13 which is appropriate to maintain a positive bias between themounting bracket 16 and the mounting arm 10 (through the locking bracket15) which operates to maintain the inner substrate 6 in contact with theouter substrate 5.

Movement of the above-described components from the closed (daytime)position to the open (nighttime) position will now be described. Aspreviously indicated, to move the mirror assembly from the closedposition (FIG. 1) to the open position (FIG. 3), a voltage is applied tothe solenoid 18. This, in turn, causes extension of the plunger 19.Initial movement of the plunger 19, and the coupling 23, causes only theslider linkage 21 to move. As the slider linkage 21 moves, the rollerbearing 20 attached to the slider linkage 21 is moved away from the topedge 15' of the locking bracket 15, removing the locking forces appliedto the support assembly. As the slider linkage 21 continues to move, theshoulder screw 14 is extended to the end of the slot 14' in the mountingarm 10. At this point, the shoulder screw 14 begins to push against themounting arm 10, causing the mounting arm 10 to rotate about the pivot13. The inner substrate 6 is in this way caused to rotate away from theouter substrate 5, and the roller bearing 20 is received within a slot15" formed in the locking bracket 15, passing the intermediate positionof FIG. 5. This continues until the mounting plate 8, the mounting arm10 and the locking bracket 15 reach their fully seated position, asshown in FIG. 3. At this point, the support assembly has been fullyrotated to its open position (FIG. 3). Typically, an angle of 35 degreesis formed for the illustrative embodiment shown, although this angle mayvary from 20 degrees to 40 degrees for other embodiments, or for otherapplications.

In implementing the foregoing, the solenoid plunger 19 is preferablyallowed to move about 0.2 inches before the shoulder screw 14 is allowedto reach the end of the slot 14' in the mounting arm 10. This is done toensure that the mounting arm 10 is completely unlocked, allowing theassembly to rotate into its open position as previously described. Thesolenoid plunger 19 will preferably then continue its travel, for anadditional 0.3 inches, until the support assembly is fully seated. Theshoulder screw 14, acting within the slot 14' in the mounting arm 10,preferably provides a moment arm of about 0.5 inches relative to thepivot 13. Linear translation of the shoulder screw 14 by approximately0.3 inches at a moment arm of 0.5 inches has been found to be sufficientto properly rotate the mounting arm 10 through the preferred angle ofapproximately 35 degrees, although such parameters are capable of changeto suit a particular application, if desired.

The return spring 25 preferably has a spring constant of 6 lbs/in. Inconjunction with the foregoing operations, the spring 25 is initiallystretched to produce a force of 2 lbs (at the locked position of theslider linkage 21), and is then stretched to produce a force of 5 lbs(at the fully extended position of the slider linkage 21). The openposition is maintained against the force of the spring 25 by thesolenoid 18, so that the support assembly is maintained in its seatedposition responsive to a continuous voltage applied to the solenoid 18(in excess of the return force of the spring 25). As an example, theforce needed to maintain the mounting assembly in the open position isapproximately 3 lbs, acting at a point which lies about 0.5 inches fromthe axis of rotation. It is important to note that small intermittentmovements of the support assembly (while in the open position) due toshock and vibration will not be observable to the driver, and that inthe event of an electrical failure, the forces of the return spring 25will overcome the solenoid 18, returning the support assembly to theclosed (daytime) position. Thus, proper operating conditions are met atall times.

Movement of the mounting assembly from the open (nighttime) position tothe closed (daytime) position is accomplished by removing the voltagefrom the solenoid 18. As a result, the return spring 25 (with an initialforce of 5 lbs) operates to pull the slider linkage 21 and the shoulderscrew 14 back to their initial, locked position, as previouslydescribed. The shoulder screw 14 preferably acts against the slot 14' inthe mounting arm 10 at a moment arm of about 0.5 inches, to rotate themounting arm 10 (and the support assembly) toward the closed position.As the support assembly is rotated (to the closed but unlocked positionof FIG. 6), the shoulder screw 14 is withdrawn from the slot 15" in thelocking bracket 15, and a lateral edge of the inner substrate 6 isbrought into contact with the outer substrate 5. The inner substrate 6will continue to close, and the mounting plate 8 will be allowed topivot at the hinge 11, until the two substrates 5, 6 are in full contactover their entire width (and length).

Even after the support assembly reaches this closed position, the sliderlinkage 21 continues to move, causing the roller bearing 20 to becomefirmly wedged against the sloped, mating surface (the top edge 15') ofthe locking bracket 15. As a result, the mounting assembly is locked inits closed position (FIG. 1), and the system is placed in equilibriumsuch that the sum of the forces acting on the roller bearing 20 equalszero.

An important aspect of the foregoing is the proper operation of, andmaintenance of the conditions established for the several componentspreviously described, particularly the solenoid 18. Preferably, thesolenoid 18 is a tubular, direct current solenoid, with a plunger 19configured for push-mode operation. FIG. 7 illustrates the preferredforce characteristics for the solenoid 18, and shows that the availableplunger force will generally increase as the plunger 19 nears its fullyseated position. In addition, the available force will increase as theduty cycle for the solenoid 18 is reduced from 100% (on all the time) to10% (off 90% of the time). The maximum power at which the solenoid 18can operate is based on the power utilized over a period of time,whether supplied at continuous (constant) levels or in relatively large,short duration pulses.

However, since the support assembly may be called upon to remain in theopen position for significant periods, a 100% duty cycle for thesolenoid 18 is required for proper operation to result.

It is further desirable, for both optical and environmental reasons, forthe mounting assembly to be closed and locked with the greatest possibleforce, to keep the substrates 5, 6 in full contact and to minimize theformation of multiple images. In the closed position, the return forceof the spring 25 determines the locking force applied to the supportassembly.

The spring 25 also establishes the initial force that the solenoid 18must produce to start the slider linkage 21 in motion (when voltage isapplied to the solenoid 18). Consequently, it is desirable to maximizethe initial (starting) force produced by the solenoid 18 withoutincreasing the size of the solenoid (i.e., typically a length of 2inches and a 1 inch diameter), and to maximize the power developed bythe solenoid 18 to maintain the support assembly in the open position.

FIG. 7 shows that the maximum available starting forces are produced ata 10% duty cycle for the solenoid, and that solenoid forces arecharacteristically at a minimum when the solenoid is in its initialposition (when operated continuously). For this reason, and to achievean optimum result, it is preferred that the solenoid 18 initiallyoperate at the high power (watts), low duty cycle (10% duty cycle) modewhich is identified at point A of FIG. 7. Once the solenoid 18 reachesits fully seated position, it is preferable to reduce the voltage and tocause the solenoid 18 to assume the continuous operating condition (100%duty cycle) identified at point B of FIG. 7.

Solenoids manufactured by "Lucas", "Guardian", "Densitron", and others,are capable of satisfying the foregoing requirements. The selectedsolenoid is preferably configured to operate at 14.0 VDC at a 10% dutycycle, and at 4.4 VDC at a 100% duty cycle. As a result, the applicationof a voltage derived from a typical vehicle battery (i.e., a voltage ofapproximately 13 volts) to the solenoid 18 will produce an initial forcein excess of 4 lbs at the plunger 19, for the mechanical configurationpreviously described. After the mounting assembly has been fully rotated(open), the solenoid voltage is preferably reduced to 4.4 VDC(continuous), producing a holding force in excess of 8 lbs for themechanical configuration previously

FIG. 8 shows a preferred schematic for implementing the above-describedelectrical functions. In this schematic, the vehicle's conventionalbattery is shown at 29. A resistor 34 is placed in series with the coilof the solenoid 18 and the battery 29. A field effect transistor 31 isplaced in shunt, across the resistor 34, and is biased responsive to aseries connected resistor 32 and capacitor 30. The gate of the fieldeffect transistor 31 is in this way biased responsive to a time constant(RC) which represents the amount of time elapsed between the initialapplication of the voltage to the system (following closure of theswitch 33) and the time at which the resistor 34 is to be shortcircuited. In its preferred embodiment, the circuit (the RC combination)is designed to short circuit the resistor 34 approximately 5 secondsafter power is first applied to the solenoid 18.

A complete system for implementing the improvements of the presentinvention is illustrated in FIG. 9, which depicts a left-side rearviewmirror. The rearview mirror which is shown incorporates the improvementspreviously described, and is mounted to a vehicle (not shown) bysuitable mounting brackets 38. The mounting brackets 38 engage pivots 37associated with the case 1 of the rearview mirror, to permit adjustmentof the rearview mirror to suit the driver. The structure of the rearviewmirror substantially corresponds to the structure previously described,and employs two mounting arms 10 for supporting the inner substrate 6.Each of the mounting arms 10 is associated with a separate solenoid 18,which is preferred to ensure proper operation of the assembly whileminimizing the size of the solenoids. A similar result could be achievedwith additional solenoids, or even a single solenoid, suitably adjustedin terms of their characteristics to provide the forces needed tooperate the inner substrate 6 as previously described.

A cable 39 connects the rearview mirror with a control panel 36. Thecable 39 includes the electrical connection extending between thesolenoids 18 and the switch 33 which operates them. The "OFF" positionrepresents an open switch 33, establishing the daytime mode of operationpreviously described. The "ON" position represents a closed switch 33,establishing the nighttime (dimmed) mode of operation previouslydescribed. Operation of the system is in this way made simple, avoidingthe need for the driver to divert attention from the road. All otheroperations are performed automatically, responsive to operation of theelectrical circuit of FIG. 8.

As an additional, and optional feature, the system of FIG. 9 furtherincludes a heater for defrosting the surface of the substrate 5.Referring to FIG. 2, such a heater is implemented with a heating element7 which is preferably formed as a capton film containing resistiveelements laminated to the rear of the inner substrate 6 (and receivedwithin a recess formed in the mounting plate 8). The cable 39 (FIG. 9)additionally includes an electrical connection for communicating withthe switch 35 provided on the control panel 36. As shown in FIG. 8, theswitch 35 and the heating element 7 with which it communicates, areplaced in series with the vehicle's battery 29. When a voltage from thebattery 29 is applied to the heating element 7, the temperature of theinner substrate 6 will rise rapidly. Contact between the substrates 5, 6will cause heat to be transferred from the inner substrate 6 to theouter substrate 5. In this way, the temperature of the outer substrate 5can be caused to rise to approximately 50° C., in about 1 minute, whichis sufficient to melt ice forming on the outer substrate 5.

FIG. 10A schematically (optically) illustrates the mirror assembly ofthe present invention in a typical (mounted) configuration as a rearviewmirror in a daytime mode of operation. As a result, the inner substrate6 is in contact with the outer substrate 5. The mirror assembly isadjusted to the comfort of the driver, in usual fashion. In thisconfiguration, light is reflected (by the inner substrate 6 and by thefront and rear surfaces of the outer substrate 5) to the driver,providing a clear view of images to the rear. Because the two substrates5, 6 (i.e., the mirrored surfaces) are in contact, the resulting imagesformed are overlapping such that double images are not perceived by thedriver. The brightness or total reflectance of the resulting image willbe the sum of the reflectance from each surface. Because the frontsurface of the outer substrate 5 is not mirrored, the image produced hassignificantly less brightness than the image produced by the mirroredsurface. As such, the image of reduced brightness is not perceived bythe driver. This substantially corresponds to the images which would bedeveloped with prior mirror assemblies, such as the mirror assemblyshown in FIG. 10B (the assembly of U.S. Pat. No. 4,371,235 has beenselected for purposes of illustration). The space between the substratesof the mirror assembly of FIG. 10B (which is provided to permit rotationof the inner substrate) has little effect on the clarity of a reflected,daytime image. However, as will be discussed more fully below, the imageproduced with the mirror assembly of FIG. 10B will be seriouslycompromised by this spacing in other ways.

FIG. 11A schematically (optically) illustrates the mirror assembly ofthe present invention in a typical (mounted) configuration as a rearviewmirror in a nighttime mode of operation. In this illustration, the innersubstrate 6 is rotated 35 degrees from the outer substrate 5. As aresult of this, a major portion of the light passing through the outersubstrate 5, to the inner substrate 6, is reflected away from thedriver. This light is either reflected back and away from the mirroredinner substrate, or is directed toward the inside of the case 1, whichis blackened so as to absorb or otherwise diffuse incident light.Because of this, such light is not seen by the driver. As a result, theonly image that the driver sees is the image (e.g., approachingheadlights) developed responsive to the reduced (and controlled)reflectance of the outer substrate 5. This is to be compared with theimage developed with prior mirror assemblies, such as the mirrorassembly shown in FIG. 11B. It has been found that the use of planeglass as an outer substrate produces images that are potentially too dimto easily discern at night. The position of the inner substrate has thepotential for producing regions of reflected light which can interferewith the driver's ability to discern the reflected images that aredesired. These disadvantages, and the manner in which the rearviewmirror assembly of the present invention operates to overcome them, willnow be discussed in greater detail.

One special consideration is that at night, it is not only important forthe mirror assembly to reduce the brightness of the headlights ofapproaching vehicles from all possible positions (primarily to therear). It is also important that any redirected light (i.e., lightreflected by the mirror assembly, or off of the side of the vehicle)should not hinder the ability of the driver to view the desired image(from the rearview mirror).

Turning first to the reflection of unwanted light, reference is made toFIGS. 11A and 11B. FIG. 11A shows that for the rearview mirror assemblyof the present invention, reflected light is diverted away from thevehicle. FIG. 11B shows that for this prior rearview mirror assembly,reflected light is directed toward the vehicle, in this case enteringthe cab of the vehicle. Because of this, the prior rearview mirror ismade susceptible to the reflection of unwanted images at night (from therear glass toward the driver), while the rearview mirror assembly of thepresent invention effectively eliminates this possibility.

A dual state mirror must be capable of use in a high reflectance mode atnight. In this situation, the substrates will be parallel to one another(both in accordance with the prior art and in accordance with thepresent invention). It therefore becomes necessary to analyze theformation of multiple images (from two parallel glass plates). To thisend, reference is made to FIG. 12 and the following theoreticaldiscussion appropriate to an understanding of this phenomenon. Ingeneral, the separation of reflected light rays to form multiple imagesis dependent upon the following parameters:

    ______________________________________                                        a1         angle of incidence of the incoming light;                          t1         thickness of the outer substrate;                                  t2         thickness of the inner substrate;                                  n1         index of refraction for air;                                       n2         index of refraction for glass substrates; and                      d          separation between the glass substrates.                           ______________________________________                                    

The separation of reflected rays of light is governed by Snell's Law,and is given by the following:

    ______________________________________                                        s(2,1) = separation between Ray1 and Ray2                                     =         (2)(t1)tan(a2)!cos(a1); where a2 is the angle of                             refraction at the surface i1, and the angle of                                incidence at the surface i2;                                         s(3,1) = separation between Ray1 and Ray3                                     =         (2)(t1)tan(a2) + (2)(d)tan(a3)!cos(a1); where a3 is                          the angle of refraction at the surface i2, and the                            angle of incidence at the surface i3;                                s(4,1) = separation of Ray1 and Ray4                                          =         (2)(t1)tan(a2) + (2)(d)tan(a3) +                                             (2)(t2)tan(a4)!cos(a1); where a4 is the angle                                 of refraction at the surface i3 and the angle of                              incidence at the surface i4.                                         ______________________________________                                    

For prior constructions such as are illustrated in FIGS. 10B and 11B,the front glass plate is fixed in position and the rear glass platerotates on a centrally positioned vertical axis. Generally, the rearglass plate can rotate by 20.5 degrees, bringing one edge of the rearglass plate in near contact with the front glass plate. The width of theglass plate will generally be 6 inches. This suggests an estimated 1inch separation between the two glass substrates, at their center (anduniformly when in parallel). Assuming a typical thickness of 0.125inches for the two plate substrates, the dual headlights of a vehicle(FIG. 13A) will produce four separate images since there will be fourinterfaces for reflected and/or transmitted light. From the foregoingequations, the respective distances between the first image and theremaining three images will be:

s(2,1)=0.077 inches,

s(3,1)=1.016 inches, and

s(4,1)=1.094 inches;

therefore,

s(4,3)=0.078 inches.

As a result, the driver observes four images, which will appear as twosets of blurred headlights (FIG. 13B).

For the mirror assembly of the present invention, the separation betweenthe substrates 5, 6 can be kept to a distance of less than 0.01 inches.Further, since the inner substrate 6 includes only one operative face(its front surface mirror), only three images will be formed for areflection of dual headlights, and the thickness of the inner substrate6 will have no effect on optical performance (because all light isreflected from the front surface only).

Assuming thicknesses for the substrates 5, 6 of the rearview mirrorassembly of FIGS. 10A and 10B (in accordance with the present invention)which correspond to those assumed for the glass plates of the priorrearview mirror assembly of FIGS. 10B and 11B (0.125 inches), therespective distances between the first image and the remaining twoimages will be:

s(2,1)=0.077 inches, and

s(3,1)=0.087 inches;

therefore,

s(3,2)=0.009 inches.

As a result, and for the mirror assembly of the present invention, thedriver observes images which are nearly overlapping (FIG. 13C),providing a much clearer image for the driver to discern. The outersubstrate 5 could be made thinner, to still further improve this opticalperformance, but the substrate would then tend to be more fragile.

Turning lastly to the brightness of the reflected image, and referringagain to FIG. 12, such brightness is primarily dependent upon thetransmissive and reflective properties at each air/glass interface i1,i2, i3 and i4, where i4 represents an interface at the rear of the innersubstrate (where pertinent). Note that the interface i4 is not a concernfor the inner substrate 6 of the present invention, which has a mirroredsurface on its front face.

In general, a fraction of the incident light will be transmitted and afraction will be reflected at each glass/air interface. For an uncoatedglass surface, typically 96% of the incident light will be transmittedand 4% will be reflected. By coating the surface of the substrate (theouter substrate 5) with single or multiple layers of suitable thinmetallic films, the respective transmissive and reflective values can beadjusted.

For the prior rearview mirror assembly of FIGS. 10B and 11B, no coatingis provided on the front or rear surface of the outer glass plate, andno adjustment of the transmissive and reflective values for such aconfiguration is possible. For the inner glass plate, a mirror coatingis described and, again, an adjustment of the transmissive andreflective values is not possible. However, the mirror assembly of thepresent invention uses an outer substrate (glass) which is well suitedto the application of coatings for adjusting the transmissive andreflective values for the outer substrate 5.

Such coatings are preferably not applied to the front surface of theouter substrate 5, but rather are applied as a thin semi-transparentcoating on the rear surface of the outer substrate 5. This allows theouter substrate 5 to provide a dimmed, reflected image, as is desiredfor typical nighttime operations. This also allows the outer substrate 5to transmit light, in turn allowing light to pass to the mirrored frontsurface of the inner substrate 6, where it is appropriately reflecteddepending upon the mode of operation involved. For example, when theinner substrate 6 is in contact with the outer substrate 5, thesesurfaces combine to produce bright, overlapping images. When the innersubstrate 6 is placed at an angle to the outer substrate 5, the twosurfaces of the substrate 5 combine to produce dimmed, substantiallyoverlapping images, while the outer surface of the substrate 6 directsremaining incident light away from the driver so that the driver canbetter discern the dimmed images which are produced.

It will be understood that various changes in the details, materials andarrangement of parts which have been herein described and illustrated inorder to explain the nature of this invention may be made by thoseskilled in the art within the principle and scope of the invention asexpressed in the claims which follow.

For example, as an alternative to the previously described rotationmechanism, separation of the substrates 5, 6 (from a closed position toan open position) can be accomplished with a DC motor, or other suitabledrives, or may be accomplished with a translating mechanism instead of arotating mechanism, if desired. In the latter case, the assemblysupporting the inner substrate 6 would be caused to translate (straight)back from the outer substrate 5 until reaching a depth that satisfiesthe optical requirements for achieving a low reflectance stateappropriate for nighttime operations. Although this option is notpresently considered to be practical for class 6, 7 and 8 truck mirrors,since the depth and aerodynamics of the case would not be compatiblewith existing mirror installations, such a configuration could be usefulfor other classes of trucks, or other vehicles having different mirrorsizes, shapes and mounting systems. Yet another alternative would be touse a mechanical mechanism for rotating (or translating) the innersubstrate 6 relative to the outer substrate 5. This could include theuse of cables (e.g., Belden cables), hand cranks (with suitable gearing)or the like extending from the cab of the vehicle to the rearview mirrorassembly. However, in the interests of convenience in use and ease ofassembly and installation, such mechanical devices are presentlyconsidered less preferred than the electrical devices previouslydescribed.

What is claimed is:
 1. A dual state mirror assembly comprising:a housinghaving an open front; a first substrate mounted to the open front of thehousing and forming an enclosure with the housing, wherein the firstsubstrate has a surface coated with material for reflecting a portion oflight incident on the surface and transmitting a remaining portion oflight incident on the surface; and a second substrate including areflective front surface and mounted within the enclosure, for movementbetween a first position in which the front surface of the secondsubstrate is in direct contact with the first substrate, to produce abright reflected image, and a second position in which the secondsubstrate forms an angle with the first substrate, to produce a dimmedreflected image; and means for moving the second substrate between thefirst position and the second position.
 2. The mirror assembly of claim1 wherein the first substrate is a coated glass plate.
 3. The mirrorassembly of claim 2 wherein a surface of the glass plate includes a thinmetal film coating.
 4. The mirror assembly of claim 3 wherein the thinmetal film coating includes a reflective metal selected from the groupconsisting of indium, tin, aluminum, chrome, nickel, oxides andcombinations thereof.
 5. The mirror assembly of claim 3 wherein the thinmetal film coating has a reflectance value of from 10% to 30%.
 6. Themirror assembly of claim 5 wherein the thin metal film coating has atransmissivity value of from 60% to 80%.
 7. The mirror assembly of claim6 having a reflectance value of about 15% and a transmissivity value ofabout 75%.
 8. The mirror assembly of claim 3 wherein the thin metal filmcoating is applied to the glass plate in regions having differentreflectance and transmissivity values.
 9. The mirror assembly of claim 3wherein the thin metal film coating is formed on an inside surface ofthe glass plate.
 10. The mirror assembly of claim 9 which furtherincludes a protective transparent coating applied to the thin metal filmcoating.
 11. The mirror assembly of claim 9 which further includes ananti-reflective coating on an outside surface of the glass plate. 12.The mirror assembly of claim 3 having a plurality of thin metal filmcoatings.
 13. The mirror assembly of claim 1 wherein the secondsubstrate is a plate material selected from the group consisting ofglass, plastic and metal, coated with a thin film.
 14. The mirrorassembly of claim 13 wherein the thin film coating has a reflectancevalue of from 60% to 95%.
 15. The mirror assembly of claim 14 whereinthe thin film coating has a reflectance value of about 90%.
 16. Themirror assembly of claim 13 wherein the thin film coating is applied tothe glass plate in regions having different reflectance andtransmissivity values.
 17. The mirror assembly of claim 1 wherein thehousing has an aerodynamic shape.
 18. The mirror assembly of claim 1wherein the angle formed between the first substrate and the secondsubstrate is from 20 degrees to 40 degrees.
 19. The mirror assembly ofclaim 18 wherein the angle is about 35 degrees.
 20. The mirror assemblyof claim 1 which further comprises an electric heating element containedwithin the housing.
 21. The mirror assembly of claim 20 wherein theelectric heating element is associated with the second substrate. 22.The mirror assembly of claim 1 wherein the moving means operatesresponsive to a solenoid.
 23. The mirror assembly of claim 22 whereinthe solenoid is a push-type, cylindrical solenoid operable responsive toan applied DC voltage.
 24. The mirror assembly of claim 1 wherein themoving means operates to rotate the second substrate relative to thefirst substrate, about a pivot point corresponding to contiguous lateraledges of the first substrate and the second substrate.
 25. The mirrorassembly of claim 1 wherein the moving means comprises:a supportassembly for receiving the second substrate and including an armextending along the support assembly; a locking assembly including amounting bracket having an end which is pivotally connected to an end ofthe arm of the support assembly, and a sliding bracket attached to themounting bracket to slide along the length of the mounting bracket; anactuator including a pivot pin for engaging an aperture formed in thesliding bracket of the locking assembly, and an aperture formed in thearm of the support assembly; and a spring attached to and extendingbetween the mounting bracket and the sliding bracket of the lockingassembly.
 26. The mirror assembly of claim 25 which further includes alocking bracket attached to and extending from the support assembly, anda roller bearing attached to the mounting bracket of the lockingassembly, for engaging a lateral edge of the locking bracket.
 27. Themirror assembly of claim 26 wherein the lateral edge of the lockingbracket includes a bevelled portion for engaging the roller bearing tolock the moving means in an open position.
 28. The mirror assembly ofclaim 25 which further includes a pivot connecting the support assemblyand the arm, and springs extending between the support assembly and thearm on opposing sides of the pivot.
 29. The mirror assembly of claim 25which further includes means attached to the mounting bracket andengaging the actuator, for moving the actuator in a longitudinaldirection along the mounting bracket.
 30. The mirror assembly of claim29 wherein the moving means is a solenoid.
 31. The mirror assembly ofclaim 30 which further includes means for operating the solenoid in afirst mode, for initiating operation of the moving means, and in asecond mode, for locking the moving means in a position such that thesecond substrate remains in contact with the first substrate.
 32. Themirror assembly of claim 31 wherein the first mode includes operatingthe solenoid at an increased voltage and at an about 10% duty cycle. 33.The mirror assembly of claim 32 wherein the second mode includesoperating the solenoid at a decreased voltage and at an about 100% dutycycle.
 34. A tandem mirror assembly for avoiding double imagescomprising:a housing having an open front; an at least partiallytransparent substrate mounted to the open front of the housing andforming an enclosure with the housing; a reflective substrate mountedwithin the enclosure and positioned in direct contact with the at leastpartially transparent substrate; and means for rotating the reflectivesubstrate about a lateral edge of the reflective substrate, and relativeto the at least partially transparent substrate.
 35. A dual state mirrorassembly comprising:a first substrate having a surface coated withmaterial for reflecting a portion of light incident on the surface andtransmitting a remaining portion of light incident on the surface; and asecond substrate including a reflective front surface, for movementbetween a first position in which the front surface of the secondsubstrate is in direct contact with the first substrate, to produce abright reflected image, and a second position in which the secondsubstrate forms an angle with the first substrate, to produce a dimmedreflected image.
 36. An apparatus for controlling a dual state mirrorincluding a first substrate having a surface for reflecting a portion oflight incident on the surface and transmitting a remaining portion oflight incident on the surface, and a second substrate including areflective surface, for movement between a first position in which thefront surface of the second substrate is adjacent to the firstsubstrate, to produce a bright reflected image, and a second position inwhich the second substrate forms an angle with the first substrate, toproduce a dimmed reflected image, the apparatus comprising:a supportassembly for receiving the second substrate and including an armextending along the support assembly; a locking assembly including amounting bracket having an end which is pivotally connected to an end ofthe arm of the support assembly, and a sliding bracket attached to themounting bracket to slide along the length of the mounting bracket; anactuator including a pivot pin for engaging an aperture formed in thesliding bracket of the locking assembly, and an aperture formed in thearm of the support assembly; and a spring attached to and extendingbetween the mounting bracket and the sliding bracket of the lockingassembly.
 37. The apparatus of claim 36 which further includes a lockingbracket attached to and extending from the support assembly, and aroller bearing attached to the mounting bracket of the locking assembly,for engaging a lateral edge of the locking bracket.
 38. The apparatus ofclaim 37 wherein the lateral edge of the locking bracket includes abevelled portion for engaging the roller bearing to lock the movingmeans in an open position.
 39. The apparatus of claim 36 which furtherincludes a pivot connecting the support assembly and the arm, andsprings extending between the support assembly and the arm on opposingsides of the pivot.
 40. The apparatus of claim 36 which further includesmeans attached to the mounting bracket and engaging the actuator, formoving the actuator in a longitudinal direction along the mountingbracket.
 41. The apparatus of claim 40 wherein the moving means is asolenoid.
 42. The mirror assembly of claim 41 which further includesmeans for operating the solenoid in a first mode, for initiatingoperation of the moving means, and in a second mode, for locking themoving means in a position such that the second substrate remains incontact with the first substrate.
 43. The mirror assembly of claim 42wherein the first mode includes operating the solenoid at an increasedvoltage and at an about 10% duty cycle.
 44. The mirror assembly of claim43 wherein the second mode includes operating the solenoid at adecreased voltage and at an about 100% duty cycle.
 45. The mirrorassembly of claim 1, wherein the moving means automatically causes thesecond substrate to move to the first position upon electrical failureof the mirror assembly.
 46. The mirror assembly of claim 45 wherein themoving means comprises one or more actuators for moving the secondsubstrate between the first position and the second position and one ormore springs for automatically moving the second substrate to the firstposition upon electrical failure of the one or more actuators.
 47. Themirror assembly of claim 1, wherein the first substrate and secondsubstrate are convex in shape.
 48. The mirror assembly of claim 1,wherein the moving means comprises self-leveling means for ensuring thatthe second substrate is parallel to the first substrate in the firstposition.
 49. The mirror assembly of claim 48, wherein the self-levelingmeans comprises two independent arms holding the second substrate andadapted to pivot the second substrate about a first leveling axis andfurther adapted to pivot the second substrate about a second levelingaxis substantially perpendicular to the first leveling axis.
 50. A dualstate mirror assembly comprising:a housing having an open front; a firstsubstrate mounted to the open front of the housing and forming anenclosure with the housing, wherein the first substrate has a surfacefor reflecting a portion of light incident on the surface andtransmitting a remaining portion of light incident on the surface; and asecond substrate including a reflective front surface and mounted withinthe enclosure, for movement between a first position in which the frontsurface of the second substrate is in direct contact with the firstsubstrate, to produce a bright reflected image, and a second position inwhich the second substrate forms an angle with the first substrate, toproduce a dimmed reflected image; and means for moving the secondsubstrate between the first position and the second position.
 51. Themirror assembly of claim 50, wherein the moving means automaticallycauses the second substrate to move to the first position uponelectrical failure of the mirror assembly.
 52. The mirror assembly ofclaim 51, wherein the moving means comprises one or more actuators formoving the second substrate between the first position and the secondposition and one or more springs for automatically moving the secondsubstrate to the first position upon electrical failure of the one ormore actuators.
 53. The mirror assembly of claim 50, wherein the firstsubstrate and second substrate are convex in shape.
 54. The mirrorassembly of claim 50, wherein the moving means comprises self-levelingmeans for ensuring that the second substrate is parallel to the firstsubstrate in the first position.
 55. The mirror assembly of claim 54,wherein the self-leveling means comprises two independent arms holdingthe second substrate and adapted to pivot the second substrate about afirst leveling axis and further adapted to pivot the second substrateabout a second leveling axis substantially perpendicular to the firstleveling axis.
 56. The mirror assembly of claim 50, wherein the secondsubstrate has a thin film coating for reflecting light incident on thesecond substrate.
 57. The mirror assembly of claim 56, wherein the thinfilm coating is applied in regions having different reflectance andtransmissivity values.